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Statistics about the structure of the atom

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Statistics about the structure of the atom

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Overview of Atomic Structure

Atoms are made up of particles called protons, neutrons, and electrons, which are responsible for the mass and charge of atoms.

Learning Objectives

Discuss the electronic and structural properties of an atom

Key Takeaways

Key Points

An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus.

Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams, which scientists define as one atomic mass unit (amu) or one Dalton.

Each electron has a negative charge (-1) equal to the positive charge of a proton (+1).

Neutrons are uncharged particles found within the nucleus.

Key Terms

atom: The smallest possible amount of matter which still retains its identity as a chemical element, consisting of a nucleus surrounded by electrons.

proton: Positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element. It weighs 1 amu.

neutron: A subatomic particle forming part of the nucleus of an atom. It has no charge. It is equal in mass to a proton or it weighs 1 amu.

An atom is the smallest unit of matter that retains all of the chemical properties of an element. Atoms combine to form molecules, which then interact to form solids, gases, or liquids. For example, water is composed of hydrogen and oxygen atoms that have combined to form water molecules. Many biological processes are devoted to breaking down molecules into their component atoms so they can be reassembled into a more useful molecule.

Atomic Particles

Atoms consist of three basic particles: protons, electrons, and neutrons. The nucleus (center) of the atom contains the protons (positively charged) and the neutrons (no charge). The outermost regions of the atom are called electron shells and contain the electrons (negatively charged). Atoms have different properties based on the arrangement and number of their basic particles.

The hydrogen atom (H) contains only one proton, one electron, and no neutrons. This can be determined using the atomic number and the mass number of the element (see the concept on atomic numbers and mass numbers).

Atomic Mass

Protons and neutrons have approximately the same mass, about 1.67 × 10⁻²⁴ grams. Scientists define this amount of mass as one atomic mass unit (amu) or one Dalton. Although similar in mass, protons are positively charged, while neutrons have no charge. Therefore, the number of neutrons in an atom contributes significantly to its mass, but not to its charge.

Electrons are much smaller in mass than protons, weighing only 9.11 × 10⁻²⁸ grams, or about 1/1800 of an atomic mass unit. Therefore, they do not contribute much to an element's overall atomic mass. When considering atomic mass, it is customary to ignore the mass of any electrons and calculate the atom's mass based on the number of protons and neutrons alone.

Electrons contribute greatly to the atom's charge, as each electron has a negative charge equal to the positive charge of a proton. Scientists define these charges as "+1" and "-1. " In an uncharged, neutral atom, the number of electrons orbiting the nucleus is equal to the number of protons inside the nucleus. In these atoms, the positive and negative charges cancel each other out, leading to an atom with no net charge.

Volume of Atoms

Accounting for the sizes of protons, neutrons, and electrons, most of the volume of an atom-greater than 99 percent-is, in fact, empty space. Despite all this empty space, solid objects do not just pass through one another. The electrons that surround all atoms are negatively charged and cause atoms to repel one another, preventing atoms from occupying the same space. These intermolecular forces prevent you from falling through an object like your chair.

Atomic Number and Mass Number

The atomic number is the number of protons in an element, while the mass number is the number of protons plus the number of neutrons.

Learning Objectives

Determine the relationship between the mass number of an atom, its atomic number, its atomic mass, and its number of subatomic particles

Key Takeaways

Key Points

Neutral atoms of each element contain an equal number of protons and electrons.

The number of protons determines an element's atomic number and is used to distinguish one element from another.

The number of neutrons is variable, resulting in isotopes, which are different forms of the same atom that vary only in the number of neutrons they possess.

Together, the number of protons and the number of neutrons determine an element's mass number.

Since an element's isotopes have slightly different mass numbers, the atomic mass is calculated by obtaining the mean of the mass numbers for its isotopes.

Key Terms

mass number: The sum of the number of protons and the number of neutrons in an atom.

atomic number: The number of protons in an atom.

atomic mass: The average mass of an atom, taking into account all its naturally occurring isotopes.

Atomic Number

Neutral atoms of an element contain an equal number of protons and electrons. The number of protons determines an element's atomic number (Z) and distinguishes one element from another. For example, carbon's atomic number (Z) is 6 because it has 6 protons. The number of neutrons can vary to produce isotopes, which are atoms of the same element that have different numbers of neutrons. The number of electrons can also be different in atoms of the same element, thus producing ions (charged atoms). For instance, iron, Fe, can exist in its neutral state, or in the +2 and +3 ionic states.

Mass Number

An element's mass number (A) is the sum of the number of protons and the number of neutrons. The small contribution of mass from electrons is disregarded in calculating the mass number. This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. Protons and neutrons both weigh about one atomic mass unit or amu. Isotopes of the same element will have the same atomic number but different mass numbers.

Scientists determine the atomic mass by calculating the mean of the mass numbers for its naturally-occurring isotopes. Often, the resulting number contains a decimal. For example, the atomic mass of chlorine (Cl) is 35.45 amu because chlorine is composed of several isotopes, some (the majority) with an atomic mass of 35 amu (17 protons and 18 neutrons) and some with an atomic mass of 37 amu (17 protons and 20 neutrons).

Given an atomic number (Z) and mass number (A), you can find the number of protons, neutrons, and electrons in a neutral atom. For example, a lithium atom (Z=3, A=7 amu) contains three protons (found from Z), three electrons (as the number of protons is equal to the number of electrons in an atom), and four neutrons (7 - 3 = 4).

Isotopes

Isotopes are various forms of an element that have the same number of protons, but a different number of neutrons.

Learning Objectives

Discuss the properties of isotopes and their use in radiometric dating

Key Takeaways

Key Points

Isotopes are atoms of the same element that contain an identical number of protons, but a different number of neutrons.

Despite having different numbers of neutrons, isotopes of the same element have very similar physical properties.

Some isotopes are unstable and will undergo radioactive decay to become other elements.

The predictable half-life of different decaying isotopes allows scientists to date material based on its isotopic composition, such as with Carbon-14 dating.

Key Terms

isotope: Any of two or more forms of an element where the atoms have the same number of protons, but a different number of neutrons within their nuclei.

half-life: The time it takes for half of the original concentration of an isotope to decay back to its more stable form.

radioactive isotopes: an atom with an unstable nucleus, characterized by excess energy available that undergoes radioactive decay and creates most commonly gamma rays, alpha or beta particles.

radiocarbon dating: Determining the age of an object by comparing the ratio of the 14C concentration found in it to the amount of 14C in the atmosphere.

What is an Isotope?

Isotopes are various forms of an element that have the same number of protons but a different number of neutrons. Some elements, such as carbon, potassium, and uranium, have multiple naturally-occurring isotopes. Isotopes are defined first by their element and then by the sum of the protons and neutrons present.

Carbon-12 (or ¹²C) contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 amu (six protons and six neutrons).

Carbon-14 (or ¹⁴C) contains six protons, eight neutrons, and six electrons; its atomic mass is 14 amu (six protons and eight neutrons).

While the mass of individual isotopes is different, their physical and chemical properties remain mostly unchanged.

Isotopes do differ in their stability. Carbon-12 ( ¹²C) is the most abundant of the carbon isotopes, accounting for 98.89% of carbon on Earth. Carbon-14 ( ¹⁴C) is unstable and only occurs in trace amounts. Unstable isotopes most commonly emit alpha particles (He ²⁺) and electrons. Neutrons, protons, and positrons can also be emitted and electrons can be captured to attain a more stable atomic configuration (lower level of potential energy ) through a process called radioactive decay. The new atoms created may be in a high energy state and emit gamma rays which lowers the energy but alone does not change the atom into another isotope. These atoms are called radioactive isotopes or radioisotopes.

Radiocarbon Dating

Carbon is normally present in the atmosphere in the form of gaseous compounds like carbon dioxide and methane. Carbon-14 ( ¹⁴C) is a naturally-occurring radioisotope that is created from atmospheric ¹⁴N (nitrogen) by the addition of a neutron and the loss of a proton, which is caused by cosmic rays. This is a continuous process so more ¹⁴C is always being created in the atmosphere. Once produced, the ¹⁴ C often combines with the oxygen in the atmosphere to form carbon dioxide. Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is incorporated by plants via photosynthesis. Animals eat the plants and, ultimately, the radiocarbon is distributed throughout the biosphere.

In living organisms, the relative amount of ¹⁴C in their body is approximately equal to the concentration of ¹⁴C in the atmosphere. When an organism dies, it is no longer ingesting ¹⁴C, so the ratio between ¹⁴C and ¹²C will decline as ¹⁴C gradually decays back to ¹⁴ N. This slow process, which is called beta decay, releases energy through the emission of electrons from the nucleus or positrons.

After approximately 5,730 years, half of the starting concentration of ¹⁴C will have been converted back to ¹⁴N. This is referred to as its half-life, or the time it takes for half of the original concentration of an isotope to decay back to its more stable form. Because the half-life of ¹⁴C is long, it is used to date formerly-living objects such as old bones or wood. Comparing the ratio of the ¹⁴C concentration found in an object to the amount of ¹⁴ C in the atmosphere, the amount of the isotope that has not yet decayed can be determined. On the basis of this amount, the age of the material can be accurately calculated, as long as the material is believed to be less than 50,000 years old. This technique is called radiocarbon dating, or carbon dating for short.

Other elements have isotopes with different half lives. For example, ⁴⁰K (potassium-40) has a half-life of 1.25 billion years, and ²³⁵ U (uranium-235) has a half-life of about 700 million years. Scientists often use these other radioactive elements to date objects that are older than 50,000 years (the limit of carbon dating). Through the use of radiometric dating, scientists can study the age of fossils or other remains of extinct organisms.

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Recall the stability associated with an atom that has a completely-filled valence shell

Construct an atom according to the Bohr model

Key Terms

Octet rule: A rule stating that atoms lose, gain, or share electrons in order to have a full valence shell of 8 electrons. (Hydrogen is excluded because it can hold a maximum of 2 electrons in its valence shell. )

Electron shell: The collective states of all electrons in an atom having the same principal quantum number (visualized as an orbit in which the electrons move).

Electron Shells

Niels Bohr proposed an early model of the atom as a central nucleus containing protons and neutrons being orbited by electrons in shells. As previously discussed, there is a connection between the number of protons in an element, the atomic number that distinguishes one element from another, and the number of electrons it has. In all electrically-neutral atoms, the number of electrons is the same as the number of protons. Each element, when electrically neutral, has a number of electrons equal to its atomic number.

An early model of the atom was developed in 1913 by Danish scientist Niels Bohr (1885-1962). The Bohr model shows the atom as a central nucleus containing protons and neutrons with the electrons in circular orbitals at specific distances from the nucleus (Figure \(\PageIndex{1}\)). These orbits form electron shells or energy levels, which are a way of visualizing the number of electrons in the various shells. These energy levels are designated by a number and the symbol "n." For example, the 1n shell represents the first energy level located closest to the nucleus.

Figure \(\PageIndex{1}\): The Bohr model postulated that electron orbited the nucleus in shells of fixed distance.

An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus. Energy from a photon of light can bump it up to a higher energy shell, but this situation is unstable and the electron quickly decays back to the ground state.

Bohr Diagrams

Bohr diagrams show electrons orbiting the nucleus of an atom somewhat like planets orbit around the sun. In the Bohr model, electrons are pictured as traveling in circles at different shells, depending on which element you have. Figure \(\PageIndex{2}\) contrast the Bohr diagrams for lithium, fluorine and aluminum atoms. The shell closest to the nucleus is called the K shell, next is the L shell, next is the M shell.

Figure \(\PageIndex{2}\): Bohr diagrams for neutral lithium, fluorine and aluminum atoms.

Each shell can only hold certain number of electrons. K shell can have 2, L can have 8 , M can have 18 electrons and so on.

Lithium has three electrons:

two go to K shell and

the remaining one goes to the L shell.

Its electronic configuration is K(2), L(1)

Fluorine has nine electrons:

two go to K shell and

the remaining seven go to the L shell.

Its electronic configuration is K(2), L(7). Note that L can have 8 electrons.

Aluminum has thirteen electrons:

two go to the K shell,

eight go to the L shell, and

remaining three go to the M shell.

Its electronic configuration is K(2), L(8), M(3). Note that the M shell can have 18 electrons.

Orbitals in the Bohr model

Electrons fill orbit shells in a consistent order. Under standard conditions, atoms fill the inner shells (closer to the nucleus) first, often resulting in a variable number of electrons in the outermost shell. The innermost shell has a maximum of two electrons, but the next two electron shells can each have a maximum of eight electrons. This is known as the octet rule which states that, with the exception of the innermost shell, atoms are more stable energetically when they have eight electrons in their valence shell, the outermost electron shell. Examples of some neutral atoms and their electron configurations are shown in Figure \(\PageIndex{3}\). As shown, helium has a complete outer electron shell, with two electrons filling its first and only shell. Similarly, neon has a complete outer 2n shell containing eight electrons. In contrast, chlorine and sodium have seven and one electrons in their outer shells, respectively. Theoretically, they would be more energetically stable if they followed the octet rule and had eight.

Figure \(\PageIndex{3}\):

Bohr diagrams

Bohr diagrams indicate how many electrons fill each principal shell. Group 18 elements (helium, neon, and argon are shown) have a full outer, or valence, shell. A full valence shell is the most stable electron configuration. Elements in other groups have partially-filled valence shells and gain or lose electrons to achieve a stable electron configuration.

An atom may gain or lose electrons to achieve a full valence shell, the most stable electron configuration. The periodic table is arranged in columns and rows based on the number of electrons and where these electrons are located, providing a tool to understand how electrons are distributed in the outer shell of an atom. As shown in , the group 18 atoms helium (He), neon (Ne), and argon (Ar) all have filled outer electron shells, making it unnecessary for them to gain or lose electrons to attain stability; they are highly stable as single atoms. Their non-reactivity has resulted in their being named the inert gases (or noble gases). In comparison, the group 1 elements, including hydrogen (H), lithium (Li), and sodium (Na), all have one electron in their outermost shells. This means that they can achieve a stable configuration and a filled outer shell by donating or losing an electron. As a result of losing a negatively-charged electron, they become positively-charged ions. When an atom loses an electron to become a positively-charged ion, this is indicated by a plus sign after the element symbol; for example, Na⁺. Group 17 elements, including fluorine and chlorine, have seven electrons in their outermost shells; they tend to fill this shell by gaining an electron from other atoms, making them negatively-charged ions. When an atom gains an electron to become a negatively-charged ion this is indicated by a minus sign after the element symbol; for example, \(F^-\). Thus, the columns of the periodic table represent the potential shared state of these elements' outer electron shells that is responsible for their similar chemical characteristics.

Lewis Symbols

Lewis Symbols are simplified Bohr diagrams which only display electrons in the outermost energy level.

Summary

In the Bohr model of the atom, the nucleus contains the majority of the mass of the atom in its protons and neutrons.

Orbiting the positively-charged core are the negatively charged electrons, which contribute little in terms of mass, but are electrically equivalent to the protons in the nucleus.

In most cases, electrons fill the lower-energy orbitals first, followed by the next higher energy orbital until it is full, and so on until all electrons have been placed.

Atoms tend to be most stable with a full outer shell (one which, after the first, contains 8 electrons), leading to what is commonly called the "octet rule".

The properties of an element are determined by its outermost electrons, or those in the highest energy orbital.

Atoms that do not have full outer shells will tend to gain or lose electrons, resulting in a full outer shell and, therefore, stability.

Contributors and Attributions

Boundless (www.boundless.com)

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Recall the stability associated with an atom that has a completely-filled valence shell Construct an atom according to the Bohr model Key Terms Octet rule: A rule stating that atoms lose, gain, or share electrons in order to have a full valence shell of 8 electrons.

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Describe and model the structure of the atom in terms of the nucleus, protons, neutrons and electrons; comparing mass and charge of protons neutrons and electrons

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Structure of the atom - The atom - GCSE Chemistry (Single Science) Revision - WJEC - BBC Bitesize

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Learn about the structure of atoms with BBC Bitesize GCSE Chemistry (WJEC).

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For this topic videos are an essential resource as we cannot physically show students an atom with protons and nuetrons only as a model so the video gives a better idea of what an atom is.

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Atomic Structure And Electrons - Structure Of An Atom - What Are Atoms - Neutrons Protons Electrons

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The Periodic Table Song (2018 Update!) | SCIENCE SONGS

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Argonne scientists prepare to load a target onto the laboratory's Low Energy Accelerator Facility, which helps to create medical isotopes. Credit: Argonne National Laboratory

Cancer is one of the most dreaded diagnoses most people can imagine receiving.

However, no two cancer patients -even if they have the same kind of cancer-experience exactly the same disease.

Successful treatment requires an approach tailored to the specific nature of an individual's disease. The more customized the therapy is, the more effective it will be at killing cancer cells and sparing healthy tissue.

One way to deliver a knockout punch to tumor cells is to use medical isotopes or radionuclides-radiologically active atoms that can provide a highly targeted dose directly at a tumor site. While not applicable for all cancers, targeted radionuclide therapy is providing doctors with a new weapon in their arsenal against cancer.

The use of radionuclides in medicine is not new: Every year, doctors perform more than 40 million medical procedures that rely on the use of medical isotopes. However, most of these procedures are currently for diagnosing disease rather than treating it.

Producing radionuclides requires specialized facilities-they can't be manufactured in just any lab. At the U.S. Department of Energy's (DOE) Argonne National Laboratory, for example, high-powered linear accelerators are dispatched to generate these radionuclides, and specialized radiological facilities are needed to purify them. Traditionally used for physics experiments, these accelerators have the capability to study and even create radionuclides for use by researchers and doctors.
How medical isotopes work
Once produced, medical radionuclides can fall into three major categories. The first is diagnostic, where the radioisotope allows doctors to visualize a tumor's precise location and contours within the body with greater clarity than an MRI scan provides. Another is therapeutic, where doctors use the radionuclide to deliver cancer-killing radiation directly to tumor cells. The third is theragnostic, which combines the power of both in such a way that the theragnostic radionuclide agent allows a doctor to both visualize and treat a tumor simultaneously.

When added into new generations of medicines that contain medical isotopes, or radiopharmaceuticals, that selectively seek out cancer cells, or that provide additional benefits in radiotherapy, these theragnostic isotopes will give doctors more options in the fight against disease and will ultimately give patients more hope.

Argonne's long history of expertise in nuclear physics, nuclear chemistry, chemical separations and accelerator physics has paid dividends in the creation of both a radionuclide research and development program and a specialized process for supplying a particular radionuclide, copper-67, to the medical community.

"Copper-67 is an especially valuable radioisotope because it is theragnostic and because we have a way to produce it in quantities that would be useful to hospitals," said Dave Rotsch, an Argonne chemist and deputy program manager of Argonne's radioisotope program. "Because Argonne has unique facilities and expertise that allow us to produce these isotopes, hospitals are expressing interest."
Argonne's critical research role
Argonne's work in radioisotopes is supported by the DOE Isotope Program, which is the global leader in producing and distributing radioactive and enriched stable isotopes that are deemed critical or are in short supply. DOE's Isotope Program is taking advantage of the capabilities found at national laboratories like Argonne and putting them to use developing advanced production and processing technologies for these much-needed isotopes.

In addition to this effort, the DOE's National Nuclear Security Administration funds Argonne to support and accelerate the U.S. production of another isotope, molybdenum-99. Argonne continues to provide target testing and development, irradiation, and Monte Carlo calculation services for multiple commercial partners to accelerate domestic production of molybdenum-99. The laboratory also helps develop and optimize separation methods for those partners.

"Argonne has a long history of showing that we can make important contributions in radioisotopes-originally in R&D, but now in actually producing them as well," said Argonne physicist and deputy program manager Jerry Nolen.

One key facility involved in producing radioisotopes is Argonne's Low-Energy Accelerator Facility (LEAF). To make medical isotopes, the LEAF delivers a powerful beam of electrons, which are converted to gamma rays, which are highly energetic photons, or packets of light.

These gamma rays, in turn, strike a highly pure, stable target material, like zinc-68. The resulting photo-nuclear reaction ejects one or more protons or neutrons to make the desired radioisotope: copper-67 in this case.

Only a small fraction of the target mass is converted to the isotope of interest, which means that the target can be used over and over again.

"It's a little bit like doing alchemy," Rotsch said. "Essentially, by hitting our target with photons, we're converting one element into another or one isotope into another."

The copper-67 and other byproduct isotopes are separated in gaseous form in a process that involves vaporizing the zinc in the target material and condensing it on a cold surface. The copper is then dissolved into a solution and further purified through a process that allows researchers to selectively isolate copper-67 (or whatever isotope they might want) based on the chemical differences of the atoms that are present in the solution.
A world of medical isotopes
Copper-67 is not the only isotope of interest being studied by researchers at Argonne. Rotsch and his colleagues are also investigating scandium-47, another exciting theragnostic isotope, and actinium-225, which has shown great promise for treating cancer.

"With most standard treatments, like chemotherapy, you don't know to which drug, or drugs, a patient will respond the best, so it can sometimes be a guess-and-check game," Rotsch said.

Radiopharmaceuticals allow doctors to observe a tumor's uptake of a diagnostic version of the radiopharmaceutical. Based on these results, Rotsch explained, the doctor can more effectively develop and prescribe a treatment plan with a therapeutic or theragnostic radiopharmaceutical.

Artificial intelligence also could help doctors pair radioisotope candidates with individual tumors. Using the genetic profile of a tumor on a computer, researchers and medical professionals could run simulations of how a radiopharmaceutical would attach to and attack the tumor. This would provide a good idea of which therapies would be most effective even before implementing them, said Kawtar Hafidi, Argonne associate laboratory director for Physical Sciences and Engineering.

"Argonne is unique in the suite of facilities and expertise that it offers, from the accelerators to the radiochemical separations to the computing," she said. "By combining all of these resources, we can really make a range of treatments more effective."

From Argonne's perspective, the ultimate goal, Hafidi said, is to create an integrated program that allows scientists to develop isotopes as fluidly as possible and create pathways for new treatments that have yet to be conceived.

"Who knows what other therapies are waiting for us on the periodic table," she said.

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Accelerating cancer treatments with the power of isotopes

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Cancer is one of the most dreaded diagnoses most people can imagine receiving. However, no two cancer patients -even if they have the same kind of cancer-experience exactly the same disease. Successful treatment requires an approach tailored to the specific nature of an individual's disease.

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Scoilnet is a great website for teachers to use in order to access and research different resources that can be used in the classroom. Teachers can upload resources they have found useful and it is split up into the different sections within the science curriculum!

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Official education portal of the Department of Education and Skills in Ireland. Curriculum focused resources and support for primary and post primary teachers.

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Phet is an interactive game that can take place in the classroom or at home

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Some videos and other lessons and ideas that teachers can be used in the class. This gives some ideas of how to teach students interactively.

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From conducting this unit of learning in the class I would definitely include a little bit more variation in my assessment techniques in the future.

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This paper is based around biology but links in well with teaching science and I used this a lot in my planning and preparation

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Interactive website for students to look at to do some extra research

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Atoms are the foundation of chemistry. They are the basis for everything in the Universe. As you know, matter is composed of atoms. Solids are made of densely packed atoms while gases have atoms that are spread out. We're going to cover basics like atomic structure and bonding between atoms. As you learn more, you can move to the reactions and biochemistry pages and see how atoms form compounds that help the biological world survive.

Are there pieces of matter that are smaller than atoms? Sure there are. Super-small particles can be found inside the pieces of atoms. These subatomic particles include nucleons and quarks. Nuclear chemists and physicists work together at particle accelerators to discover the presence of these tiny, tiny, tiny pieces of matter. However, science is based on the atom because it is the smallest distinct unit of matter.

Even though many super-tiny atomic particles exist, you only need to remember the three basic parts of an atom: electrons, protons, and neutrons. What are electrons, protons, and neutrons? Electrons are the smallest of the three particles that make up atoms. Electrons are found in shells or orbitals that surround the nucleus of an atom. Protons and neutrons are found in the nucleus. They group together in the center of the atom. That's all you have to remember. Three easy pieces!

There are almost 120 known elements in the periodic table. (117 as we write this) Chemists and physicists are trying to make new ones every day in their labs. The atoms of different elements have different numbers of electrons, protons, and neutrons. Every element is unique and has an atomic number. That number tells you the number of protons in every atom of the element. The atomic number is also called the proton number.

You can see that each part of the atom is labeled with a "+", "-", or a "0." Those symbols refer to the charge of the particle. Have you ever heard about getting a shock from a socket, static electricity, or lightning? Those are all related to electric charges. Charges are also found in tiny particles of matter.

The electron always has a "-", or negative, charge. The proton always has a "+", or positive, charge. If the charge of an entire atom is "0", or neutral, there are equal numbers of positive and negative charges. Neutral atoms have equal numbers of electrons and protons. The third particle is the neutron. It has a neutral charge, also known as a charge of zero.

Since the number of protons in an atom does not change, fewer or extra electrons can create a special atom called an ion. Cations have fewer electrons and have a positive charge. Anions have extra electrons that create a negative charge.

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Chem4Kids.com! This tutorial introduces atomic structure in chemistry. Other sections include matter, elements, the periodic table, reactions, and biochemistry.

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This is an example of a planning document that could be used when starting this unit to include your main aims for the unit.